The present invention relates to blood coagulation tests and particularly to such tests performed in vitro.
It is desirable to assess and monitor blood characteristics including hemostasis (cessation of venous or arterial bleeding), clotting or thrombus formation, and thrombolysis (dissolving clots in the blood stream) for a variety of medical procedures as for example treating blood disorders such as hemophilia, performing surgery, and blood transfusions. Such blood assessments are required promptly for surgical procedures, emergency room treatments, or blood transfusions and must be performed without the benefit of laboratory test conditions. In addition, aging and handling of a blood sample have significant effect on the blood clotting mechanism. Therefore it is necessary to provide a simple, on-site technique for in vitro assessment of blood characteristics as soon as practicable after a blood sample is drawn. The technique must also provide reliable, reproducible results.
European Patent Application No 84/304055.1 dated Jun. 15, 1984, PCT International Application No PCT/GB87/00633 and U.S. Pat. No. 5,047,211 disclose techniques for in vitro assessment of blood specimens. In those techniques, a blood sample is placed in a reservoir or container and passed through a capillary tube into a waste collection container. Blood flow through the tube is established under constant pressure (60 mm Hg), temperature (37 deg. C.) and flow rate simulating venous conditions. The capillary tube is punctured to establish bleeding and to allow for hemostasis to occur, i.e., the formation of a platelet plug in the tube puncture and cessation of bleeding. Blood pressure in the tube drops when the puncture occurs and rises gradually as the platelet plug forms in the puncture opening. The time required for full pressure recovery is observed and provides an index of the hemostasis characteristic of the blood sample. By placing a fragment of collagen (catgut, for example) in the tube the platelet collagen interaction can be assessed for a native (non anti-coagulated) blood sample.
Those patent documents reveal a number of measures and precautions taken to assure reliability and repeatability of blood assessment results, and to assure that in vitro conditions conform as nearly as possible to in vivo.
Manipulation of the blood sample must be held to a minimum because agitation or turbulence of the sample between patient and test reservoir as, for example, by transferring the sample from a collection syringe to a test reservoir, can cause release of ADP (adenosine diphasphate) in the sample and initiate the clotting/hemostasis process. Pumping the blood causes severe damage to corpuscles and inconsistent results. On the other hand, as noted in EPO application '055, the blood sample must not be allowed to settle in a test reservoir because settling of blood solids effects hemostasis. Accordingly, the blood collecting container is used as the sample reservoir to minimize sample manipulation and turbulence. Additionally, the sample in the reservoir is stirred and pressurized by introducing a blood-immiscible hydrocarbon oil (paraffin) into the bottom of the reservoir. The paraffin oil is supplied under pressure for gently stirring the sample and for simulating in vivo pressure of 60 mm Hg in the reservoir and capillary tube of the test apparatus. The PCT patent document discloses an elaborate pressure regulator apparatus for assuring that constant pressure is applied to the test reservoir and capillary tube through the paraffin supply line.
In carrying out sample assessment, it is necessary to establish a steady flow rate of the sample through the capillary tube in order to determine a pressure datum for observing the hemostasis characteristic. Accordingly, the waste receptacle is filled with paraffin so that waste blood entering the receptacle via the capillary tube displaces a like volume of paraffin in order to maintain a constant back pressure and a steady flow rate through the capillary tube. A pressure transducer fitted to the waste receptacle measures pressure variations in the system and particularly in the tube. When blood flow is established and a pressure datum recorded at a value of 60 mm Hg, the tube is ready to be punctured.
In order to achieve repeatable blood assessment results, it is necessary for the test apparatus to puncture the capillary tube with a hole of constant size each time a blood test is performed. Therefore, puncture needle size and tube size must be standardized. In addition, the tube as well as needle must be precisely positioned and firmly held when puncture occurs. Any variation in hole geometry or contour will effect pressure measurements as well as the formation of a platelet plug in the capillary tube during hemostasis.
The capillary tube in the vicinity of the puncture is continually washed by a saline solution so that blood dripping and collecting outside the tube hole does not contribute to platelet plug formation. Accordingly the disclosed patent apparatus is provided with a saline wash system for cleansing waste blood from the exterior of the capillary tube in the vicinity of the puncture. The USA and PCT patent documents provide parallel test channels so that hemostasis, thrombolysis and collegen platelet interaction assessments can be performed at the same time. This parallel facility does require duplication of the assessing apparatus for each of the test channels.
Bloods specimens can communicate contagious diseases and they must be safely discarded. The disclosed patent techniques require disposal of the blood specimen together with contaminated paraffin, saline solution, punctured tubing, piercing needles, syringes and so forth. The '211 patent provides for disposal of an entire cassette embodying parallel channels for performing blood assessments. The spent blood sample, saline solution and paraffin are discarded along with the casette.
In summary, apparatus for accurate and repeatable in vitro assessment of blood characteristics must minimize manipulation, agitation, and mechanical stress of the sample; not allow the sample to settle in its collection reservoir; establish venous or arterial conditions of pressure, temperature, and flow rate; assess a blood sample as soon as possible after collection; provide a precise capillary tube aperture; and provide safe disposal of waste blood and contaminated components.